This invention relates to an arrangement for farming fish, shell fish and other marine beings, and more particularly to a formed enclosure such as a bag of preferably circular cross-section in the horizontal plane, which is submerged into surrounding water with an open edge of the bag supported at the water
Prior art arrangements for fish farming can be two categories: open water-based enclosures, and closed land-based plants. Open enclosures are used mostly for farming consumer fish while land-based plants are filled with fresh water and are used mostly for farming fry. Open water enclosures are far less expensive than land-based plants, and are also cheaper to operate since the land-based plants typically require large, costly and power consuming pumps for conveying water into an on-shore basin.
Prior art open water enclosures are typically formed from bags comprised of net cloth which are submerged in the ocean. Natural water currents cause the water within the bags to circulate. Open water enclosures are very popular in Norway since the Gulf Stream carries relatively warm water up along the coast in the western and northern part of the country, and relatively strong tides provide sufficient current to facilitate constant circulation of water.
One disadvantage of prior art open enclosures is that the farmed fish are subject to contamination by contagious matter and parasites which may be carried by the circulating water. Another disadvantage is that the net cloth has a tendency to become clogged over time, thus requiring frequent cleaning. In order to clean the cloth, the fish are emptied and the cloth is hoisted above the water and manually scrubbed. It has been discovered that this time consuming net cleaning procedure is responsible for a major portion of the expenses incurred in the operation of prior art open enclosure fish farming installations.
An additional disadvantage of open water enclosures is that it is difficult to adjust and control the water temperature, which typically conforms to the ambient temperature of the water surrounding and infiltrating the bag. Hence, open water enclosures cannot be used in coastal districts where the water is too cold during the winter, or where the surface water is contaminated or contains damaging algae or similar matter. Nor can such prior art open water enclosures be used in districts where the surface water is too warm.
Furthermore, it has been found that fish excrement and unconsumed food particles tend to fall to the bottom of the net where they decay, causing bubbles of H.sub.2 S and methane gas to rise within the nets. These gases are very harmful to the farmed fish and may in some cases cause death.
There have been instances reported of large schools of jelly fish carried by natural currents, becoming entangled in the nets and causing the farmed fish to suffocate due to a lack of circulated fresh water.
In the event that fish farmed by means of an open water enclosure become infected with disease or parasites, the disease can spread quickly to neighboring enclosures which are usually placed relatively close by. Administering medicine to the farmed fish in such prior art open water enclosures has also been found to be problematic since the medicine dissipates and washes away quickly as a result of the natural water currents.